CN105156103A - Debris-core-borehole-reservoir multiscale shale reservoir three-dimensional fracturing evaluation method - Google Patents

Abstract

The invention relates to a debris-core-borehole-reservoir multiscale shale reservoir three-dimensional fracturing evaluation method. The method comprises the steps of: (S1) calculating mineral content brittleness indexes in a shale coring position; (S2) building relations among an internal friction angle, I type and II type fracture toughness and rock mechanical parameters; (S3) building shale fracturing evaluation models comprehensively considering a mineral content, elastic parameters, the internal friction angle, a critical strain energy release rate and the rapture toughness; (S4) applying a support vector machine algorithm to obtain a cluster analysis mode between a reservoir fracturing performance and the elastic parameters; and (S5) applying the cluster analysis mode and a reservoir three-dimensional elastic parameter data body to obtain a debris-core-borehole-reservoir multiscale shale reservoir three-dimensional fracturing model. The method can be applied to obtain the fracturing performance of any space position in a shale reservoir, so that the well position selection blindness is prevented, and the fracturing modification effect and the after-pressing yield are improved.

Description

A cutting-core-wellbore-reservoir multi-scale 3-D fracturing evaluation method for shale reservoirs

technical field

The invention belongs to the technical field of shale oil and gas development, and in particular relates to a three-dimensional fracturing evaluation method for shale reservoirs with multiple scales of cuttings-core-wellbore-reservoir.

Background technique

With the continuous and rapid growth of my country's national economy, the demand for energy has increased sharply, and the contradiction between supply and demand of oil and natural gas resources has become prominent. my country's shale gas resources are very rich. According to the latest research results of the Oil and Gas Center of the Ministry of Land and Resources in 2012, the recoverable resources of shale gas in my country are 25 trillion cubic meters, and the development potential is huge. With the successful development of typical shale gas fields such as Barnett and Eagle Ford in the United States and Fuling in my country, shale gas is expected to become an important alternative energy source. However, the development of shale gas in my country generally has bottlenecks such as high cost per well, low overall production, and uneven post-pressure effects. Coupled with the sharp drop in international oil prices, the development of shale gas resources in my country is facing investment The difficulty of recovering the cost seriously restricts the development of the shale gas industry.

The shale gas reservoirs in the United States have flat landforms, shallow burial, and uniform reservoir physical properties. Usually, the perforation cluster locations and fracturing intervals are selected by comparing the fracturing properties of each location of the horizontal wellbore, and the post-fracturing effect is better. . However, due to the severe geological structure and complex geological conditions of reservoirs in Sichuan area, the internal physical properties and heterogeneity of shale reservoirs are quite different. The existing brittleness index evaluation methods only belong to the wellbore scale and cannot realize the prediction of the brittleness of the entire reservoir. , if the wellbore trajectory of the horizontal well is located in a reservoir with poor brittleness or encounters a brittle interlayer with a high elastic modulus and a small Poisson's ratio, it will be difficult to achieve volume fracturing with the perforation position and fracturing interval optimized by the existing method. Due to the required fracture network, the production capacity of shale gas wells cannot reach the expected target, and even part of the well pressure does not see gas, which makes it difficult to return the huge investment in early drilling and large-scale hydraulic fracturing. In order to optimize the design of the trajectory of the long horizontal section of the shale gas well, so that the long horizontal section of 1000-2000m is located in a position with good reservoir physical properties and fracturing properties, a three-dimensional fracturing model of the entire reservoir must be established.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art, provide a cuttings-core-wellbore-reservoir multi-scale shale reservoir three-dimensional fracturability evaluation method, and establish a three-dimensional fracturability evaluation method for shale reservoirs sex model. Combined with geological sweet spots, in-situ stress and natural fracture development, this model can be used to guide the wellbore trajectory design of shale gas horizontal wells, and provide theoretical support for the optimization of perforation cluster positions and fracturing intervals to form maximum fractures network, improve the final fracturing effect, and recover the investment cost of shale gas wells as soon as possible.

The purpose of the present invention is achieved through the following technical solutions, a cuttings-core-borehole-reservoir multi-scale shale reservoir three-dimensional fracturability evaluation method, comprising the following steps:

S1. Using the empirical formula for mineral content brittleness index evaluation, calculate the mineral content brittleness index at the shale coring position;

S2. Establishing the relationship between the internal friction angle, the fracture toughness of type I and type II fractures, and the characteristic parameters of rock mechanics;

S3. Establish a shale fracturability evaluation model that comprehensively considers mineral content, elastic parameters, internal friction angle, critical strain energy release rate and fracture toughness, and calculate the fracturability longitudinal curve of the reservoir at the drilling position;

S4. Use the support vector machine algorithm to obtain the cluster analysis relationship between the fracturability and elastic parameters of the reservoir, and use the vertical curve of the fracturability of a single well to verify the cluster analysis between the fracturability and elastic parameters model;

S5. Apply the cluster analysis model to the three-dimensional elastic parameter data volume of the reservoir, and establish a three-dimensional fracturing model of the shale reservoir based on the multi-scale of cuttings-core-wellbore-reservoir.

Further, the step S3 includes the following sub-steps:

S31. Using the elastic parameter brittleness index evaluation empirical formula, calculate the elastic parameter brittleness index EE _n at the coring position;

S32. Establishing a comprehensive consideration of the mineral content brittleness index B _n in the step S1, the elastic parameter brittleness index EE _n and the internal friction angle in the step S2 Shale fracturing evaluation model of critical strain energy release rate G _C and fracture toughness:

In the formula, FI ₁ and FI ₂ are the fracturing evaluation indexes considering the strain energy release rate and fracture toughness of shale, respectively, dimensionless;

w is a weight coefficient with a value ranging from 0 to 1, dimensionless;

is the brittleness expression of comprehensive mineral content brittleness index B _n and elastic parameter brittleness index EE _n , B _nn is the shale brittleness index of comprehensive mineral content and elastic parameter, dimensionless; both B _n and EE _n are dimensionless;

is the weight expression of critical strain energy release rate, G _{C_n} is the weight of strain energy release rate of sandstone reservoir, dimensionless; G _C , G _{C_max} , G _{C_min} are critical strain energy release rate of sandstone reservoir, sandstone reservoir Maximum critical strain energy release rate and minimum critical strain energy release rate, in N/m;

is the weight expression of internal friction angle, is the weight of internal friction angle of sandstone reservoir, dimensionless; Respectively, the sine value of the internal friction angle at the calculated position of the sandstone reservoir, the sine value of the maximum internal friction angle and the sine value of the minimum internal friction angle of the sandstone reservoir, dimensionless;

is the weight expression of type I fracture toughness, K _{IC_n} is the weight of type I fracture toughness of sandstone reservoir, dimensionless; K _IC , K _{IC_max} , K _{IC_min} are respectively The maximum type I fracture toughness and the minimum type I fracture toughness, the unit is MPa·m ^1/2 ;

is the weight expression of type II fracture toughness, K _{IIC_n} is the weight of type II fracture toughness of sandstone reservoir, dimensionless; K _IIC , K _{IIC_max} , K _{II_min} are the type II fracture toughness and sandstone reservoir The maximum type II fracture toughness and the minimum type II fracture toughness, the unit is MPa m ^1/2 ;

S33. Using the established comprehensive multi-factor fracturing evaluation model, combining the logging data of shale gas wells and the relationship between the internal friction angle, type I and type II fracture toughness and rock mechanical characteristic parameters in step S2 Relational formula to calculate the fracability longitudinal curve characteristics of reservoirs at shale gas drilling locations.

Further, the step S4 includes:

Using the support vector machine algorithm, considering the reliability of seismic inversion reservoir elastic parameters, the compressional wave impedance, shear wave impedance, Poisson's ratio, and the ratio of Lame parameter to shear modulus are selected as elastic parameters for cluster analysis training. The classification relationship between shale reservoir fracturability and shale elastic parameters, find out the cluster analysis mode between reservoir elastic parameters and fracturability, and use the single well fracturability in step S3 The cluster analysis pattern between fracturability and elastic parameters is verified by the longitudinal curves.

Further, the step S5 includes:

Preprocessing the pre-stack seismic data volume to ensure the quality of the data volume and obtain the three-dimensional reservoir elastic parameter data volume, using the single well fracturability longitudinal curve established in the step S3, by applying the aggregation in the step S4 From the similar analysis model to the three-dimensional reservoir elastic parameter data volume, a three-dimensional fracturing model of shale reservoir based on cuttings-core-wellbore-reservoir multi-scale is established.

The present invention has the following advantages:

1. Established a three-dimensional fracturing evaluation model for shale gas reservoirs. This model can truly and accurately quantify the fracturing properties of different spatial locations of the reservoir. Combined with geological sweet spots, shale gas horizontal wells always encounter High-yield and high-fracturability layers can make up for the lack of understanding of geological conditions to a certain extent, improve the effect of volume fracturing in shale reservoirs, maximize the productivity of shale gas wells, and reduce the investment cost of shale gas wells. recovery time;

2. Use the established model to evaluate the fracturing performance at the drilling position of a single well, and optimize the perforation cluster position and fracturing interval;

3. Using the established model, the wellbore trajectory can always be located inside the highly fracturable reservoir, and the drilling speed can be increased when the drill bit drills in the highly fracturable reservoir, shortening the drilling cycle and saving drilling costs.

Description of drawings

Fig. 1 is a flow chart of a cuttings-core-wellbore-reservoir multi-scale shale reservoir three-dimensional fracturability evaluation method of the present invention;

Fig. 2 is the mineral content brittleness index curve figure of the wellbore drilling position place reservoir among the present invention;

Fig. 3 is the curve diagram of the elastic parameter brittleness index of the reservoir at the wellbore drilling position in the present invention;

Fig. 4 is a vertical curve diagram of the fracability of the reservoir at the drilling position with comprehensive consideration of mineral content, elastic parameters, internal friction angle, and critical strain energy release rate in the present invention;

Fig. 5 is a longitudinal sectional view of the cluster analysis mode based on reservoir elastic parameters and fracturing in the present invention;

Fig. 6 is a three-dimensional fracturing vertical sectional view of a shale reservoir established in the present invention;

Fig. 7 is a three-dimensional fracturability transverse cross-sectional view of a shale reservoir established in the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

A cuttings-core-wellbore-reservoir multi-scale three-dimensional fracturing evaluation method for shale reservoirs, comprising the following steps:

S1. Using X-ray diffractometer and other testing equipment, carry out the mineral composition test of drilling cuttings and sampled core fragments in the target block, and use Wang and Gale's empirical formula for mineral content brittleness index B _n evaluation (Wang, FP, and J. FWGale. Screening criteria for shale-gas systems: Gulf Coast Association of Geological Societies Transactions, v.59, p.779-793, 2009):

B _n = (W _{quartz, calcite} + W _dolomite )/W _{total mass} (1) Calculate the mineral content brittleness index B _n of shale at the drilling position or coring position, dimensionless, where W _{quartz and calcite} are quartz and the mass of calcite, W _dolomite is the mass of dolomite in Kg; W _{total mass} is the total mass of minerals in Kg; combined with the corrected mineral content curve, the mineral content brittleness of the reservoir at the drilling position of the wellbore is calculated The exponential curve is shown in Figure 2;

S2. Use a high temperature and high pressure triaxial rock mechanics testing system to test the uniaxial and triaxial rock mechanical strength parameters of shale cores, including elastic modulus E, Poisson's ratio v, and internal friction angle et al. measured the tensile strength, type I and type II fracture toughness K _IC and K _IIC of shale samples using the Brazilian disc experiment, and established the internal friction angle The relationship between mode I and II fracture toughness and rock mechanical characteristic parameters:

In the formula, σ _t is the tensile strength of tight sandstone, in MPa; σ _n is the normal confining pressure of the fracture surface, in MPa; ρ is the density of tight sandstone, in Kg/m ³ .

S3. Using Rickman’s empirical formula for mineral content brittleness index evaluation (RickmanR, MullenM, PetreE, et al.APracticalUseofShalePetrophysicsforStimulationDesignOptimization:AllShalePlaysAreNotClonesofttheBarnettShale.SPE115258,SPEAnnualTechnicalConferenceandExhibition,21-24September,Denver,Colorado200,USA), the location of the elastic calculation parameters Brittleness index EE _n , dimensionless:

${\mathrm{<span\; class="notranslate">\; EE</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, E _n is the elastic parameter brittleness index, dimensionless; E, E _max and E _min are the elastic modulus of tight sandstone reservoir, the maximum elastic modulus and the minimum elastic modulus in tight sandstone reservoir, respectively, in GPa,

ν _n is Poisson's ratio brittleness index, dimensionless; ν, v _max and v _min are Poisson's ratio of tight sandstone reservoir, maximum Poisson's ratio and minimum Poisson's ratio of tight sandstone reservoir, respectively, dimensionless. Well data, calculate the elastic parameter brittleness index curve of the reservoir at the drilling position of the wellbore, as shown in Figure 3;

Establishing a shale fracturing property that comprehensively considers the mineral content brittleness index B _n , the elastic parameter brittleness index EE _n in the step S1, and the internal friction angle, critical strain energy release rate G _C , and fracture toughness in the step S2 Evaluation model:

In the formula, FI ₁ and FI ₂ are the fracturing evaluation indexes considering the strain energy release rate and fracture toughness of shale, respectively, dimensionless;

w is a weight coefficient with a value ranging from 0 to 1, dimensionless;

is the brittleness expression of comprehensive mineral content brittleness index B _n and elastic parameter brittleness index EE _n , B _nn is the shale brittleness index of comprehensive mineral content and elastic parameter, dimensionless; the units of B _n and EE _n are dimensionless;

is the weight expression of critical strain energy release rate, G _{C_n} is the weight of strain energy release rate of sandstone reservoir, dimensionless; G _C , G _{C_max} , G _{C_min} are critical strain energy release rate of sandstone reservoir, sandstone reservoir Maximum critical strain energy release rate and minimum critical strain energy release rate, in N/m;

is the weight expression of internal friction angle, is the weight of internal friction angle of sandstone reservoir, dimensionless; Respectively, the sine value of the internal friction angle at the calculated position of the sandstone reservoir, the sine value of the maximum internal friction angle and the sine value of the minimum internal friction angle of the sandstone reservoir, dimensionless;

is the weight expression of type I fracture toughness, K _{IC_n} is the weight of type I fracture toughness of sandstone reservoir, dimensionless; K _IC , K _{IC_max} , K _{IC_min} are respectively The maximum type I fracture toughness and the minimum type I fracture toughness, the unit is MPa·m ^1/2 ;

is the weight expression of type II fracture toughness, K _{IIC_n} is the weight of type II fracture toughness of sandstone reservoir, dimensionless; K _IIC , K _{IIC_max} , K _{II_min} are the type II fracture toughness and sandstone reservoir The maximum type II fracture toughness and the minimum type II fracture toughness, the unit is MPa m ^1/2 ;

Using the established comprehensive multi-factor fracturing evaluation model, combined with logging data of shale gas wells, mineral content brittleness index B _n , elastic parameter brittleness index EE _n , internal friction angle, tensile strength, type I and type II The relationship between fracture toughness and rock mechanical characteristic parameters (2), and the calculation of the fracturability longitudinal curve of the reservoir at the shale gas drilling location are shown in Fig. 4.

S4. Using the support vector machine algorithm, considering the reliability of seismic inversion of elastic parameters of the reservoir, choose the compression wave impedance Zp, the unit is kg m ^-2 s ^-1 , the shear wave impedance Zs, the unit is kg m ^-2 · s ^-1 , Poisson's ratio ν, dimensionless, the ratio of Lame parameter and shear modulus μ/λ is used as the elastic parameter for cluster analysis training, and the relationship between the fracturability of the shale reservoir and the shale elastic parameter in the training Classification relationship, to find out the cluster analysis mode between reservoir elastic parameters and fracturing properties, as shown in Figure 5, it is found that the obtained cluster analysis mode is in good agreement with the calculation results of standard wells.

S5. Preprocess the pre-stack seismic data volume to ensure the quality of the data volume and obtain the three-dimensional reservoir elastic parameter data volume. Using the established vertical curve of single well fracturing as shown in Figure 4, apply cluster analysis From the model (Fig. 5) to the 3D reservoir elastic parameter data body, a 3D fracturability model of shale reservoir based on multi-scale cuttings-core-borehole-reservoir is established, as shown in Fig. Fracturing vertical sectional view, Figure 7 is a 3D fracturing lateral sectional view of shale reservoirs, from Figures 6 and 7, it can be seen more intuitively where the reservoir space area is more fracturable , the layout of shale gas horizontal wells should preferably consider this area, so that volume fracturing can form a maximized fracture network and improve the final effect of fracturing.

Claims (4)

1. the shale reservoir three-dimensional pressure break evaluation method that landwaste-rock core-well-reservoir is multiple dimensioned, it is characterized in that, it comprises the following steps:

S1, adopt mineral content brittleness index to evaluate empirical formula, calculate shale and to core the mineral content brittleness index of position;

S2, set up angle of internal friction, I type and the relational expression between II type crack fracture toughness and rock-mechanics property parameter;

S3, set up and consider the shale pressure break evaluation model of mineral content, elastic parameter, angle of internal friction, strain energy release rate and fracture toughness, for calculating the pressure break Vertical Curve of drilling well position reservoir;

S4, utilization algorithm of support vector machine, obtain the cluster analysis relation between reservoir pressure break and elastic parameter, and adopt the cluster analysis pattern between individual well pressure break Vertical Curve checking pressure break and elastic parameter;

S5, application cluster analysis pattern, to reservoir three dimensional elasticity supplemental characteristic body, are set up based on the multiple dimensioned shale reservoir three-dimensional pressure break model of landwaste-rock core-well-reservoir.

2. the shale reservoir three-dimensional pressure break evaluation method that a kind of landwaste-rock core-well-reservoir according to claim 1 is multiple dimensioned, it is characterized in that, described step S3 comprises following sub-step:

S31, employing elastic parameter brittleness index evaluate empirical formula, calculate the elastic parameter brittleness index EE of position of coring _n;

The mineral content brittleness index B that S32, foundation consider in described step S1 _n, elastic parameter brittleness index EE _nwith the angle of internal friction in described step S2 strain energy release rate G _cwith the shale pressure break evaluation model of fracture toughness:

In formula, FI ₁, FI ₂be respectively the pressure break evaluation number considering shale strain energy rate and fracture toughness, dimensionless;

W is the weight coefficient of number range 0 ~ 1, dimensionless;

for comprehensive mineral content brittleness index B _nwith elastic parameter brittleness index EE _nfragility expression formula, B _n-nfor the shale brittleness index of comprehensive mineral content and elastic parameter, dimensionless; B _n, EE _nequal dimensionless;

for strain energy release rate weight expression formula, G _{c_n}for the strain energy rate weight of sandstone reservoir, dimensionless; G _c, G _{c_max}, G _{c_min}be respectively the strain energy release rate of sandstone reservoir, the maximum strain energy release rate of sandstone reservoir and minimum critical strain energy rate, unit is N/m;

for angle of internal friction weight expression formula, for the angle of internal friction weight of sandstone reservoir, dimensionless; be respectively sandstone reservoir and calculate the sine value of position angle of internal friction, the sine value of maximum angle of internal friction of sandstone reservoir and the sine value of minimum angle of internal friction, dimensionless;

for I type fracture toughness weight expression formula, K _{iC_n}for the I type fracture toughness weight of sandstone reservoir, dimensionless; K _iC, K _{iC_max}, K _{iC_min}be respectively sandstone reservoir and calculate the I type fracture toughness of position, the maximum I type fracture toughness of sandstone reservoir and minimum I type fracture toughness, unit is MPam ^1/2;

for II type fracture toughness weight expression formula, K _{iIC_n}for the II type fracture toughness weight of sandstone reservoir, dimensionless; K _iIC, K _{iIC_max}, K _{iI_min}be respectively sandstone reservoir and calculate the II type fracture toughness of position, the maximum II type fracture toughness of sandstone reservoir and minimum II type fracture toughness, unit is MPam ^1/2;

The comprehensively multifactor pressure break evaluation model that S33, utilization are set up, in conjunction with angle of internal friction, I type and the relational expression between II type fracture toughness and rock-mechanics property parameter in the log data of shale gas well and described step S2, calculate the pressure break Vertical Curve feature of shale gas drilling well position reservoir.

3. the shale reservoir three-dimensional pressure break evaluation method that a kind of landwaste-rock core-well-reservoir according to claim 1 is multiple dimensioned, it is characterized in that, described step S4 comprises:

Adopt algorithm of support vector machine, consider the reliability of seismic inversion reservoir elastic parameter, select p-wave impedance, S-wave impedance, poisson's ratio, the elastic parameter that Lame parameter is trained as cluster analysis with the ratio of modulus of shearing, classification relation between training shale reservoir pressure break and shale elastic parameter, find out the cluster analysis pattern between reservoir elastic parameter and pressure break, and adopt the cluster analysis pattern in described step S3 between individual well pressure break Vertical Curve checking pressure break and elastic parameter.

4. the shale reservoir three-dimensional pressure break evaluation method that a kind of landwaste-rock core-well-reservoir according to claim 1 is multiple dimensioned, it is characterized in that, described step S5 comprises:

Pretreatment is carried out to guarantee data volume quality and to obtain three-dimensional reservoir elastic parameter data volume to earthquake data before superposition body, the individual well pressure break Vertical Curve utilizing described step S3 to set up, by applying cluster analysis pattern in described step S4 to three-dimensional reservoir elastic parameter data volume, set up based on the multiple dimensioned shale reservoir three-dimensional pressure break model of landwaste-rock core-well-reservoir.